Looks like just the common GM alternator case, looks the same as the 80's Chevy's came out with.... Stator doesn't look good at all, might be best to just get a new alternator then either polish that case or switch the new innards to the polished case on the old alternator. Then just remove the plug and your alternator will be the standard 3 wire GM alternator....

Welcome to CHR, very good looking truck!!!!